Replacing the Battery on the GPS Board
There have been two GPS boards used in the NexStar 8/9.25/11 GPS scopes.
The first was manufactured by Motorola and appeared in the earliest NexStar
8 and 11 GPS models. More recently, Celestron switched to a board they designed
in-house. Thus, all newer models have the Celestron board.
The CN-16 unit for the "i" series, AS-GT, CGEM, CGE and CGE Pro series uses the
Celestron-designed board as found in the newer NexStar GPS scopes.
As described in
this article, the older GPS modules have a battery which is rechargeable. During
normal use of the scope, the battery is charged by the 12 volts supplied to
the mount. When the battery loses its charge, the hand control will
display the incorrect time until a GPS link is established (normally the GPS
module maintains correct time between uses of the scope). The GPS link
will also take longer than normal. The original
board requires at least 40 hours to completely recharge the battery, while
the new board requires 24 hours. Disconnect the hand control (to
prevent the scope from tracking while you are away) and power up the scope
to charge the battery.
If the battery will no longer hold a charge, it will be necessary to
Click any of the pictures below for a larger version.
|The GPS board for the older NexStar GPS
telescopes is found inside
the base. Using a 3.5mm or 9/64 inch hex wrench, completely
loosen the five screws securing the plastic base cover - the cover
with the Aux, Auto Guide, and PC ports. It is not necessary to remove
the screws as we will only be lifting the cover, not completely
removing it. If you do remove the screws, note that the one in the
back is shorter than the rest.
Carefully lift the base cover. Wires run from the cover to the base
and only allow the cover to be raised about 2 inches (5cm). Put a
rolled-up sock in both gaps between the cover and each fork arm to
hold it in place. The GPS board is on the side opposite the
panel with all the connector ports. The front board shown here
is the GPS board. It is held in place by the two cross-tip
screws in the corners. As you remove these screws and pull the
board free, note the connectors on the back side of the board as well
as the antenna cable. Be sure not to drop the screws into the
The battery is held in a clip and is easily replaced. The
battery is a Panasonic ML621 - the one without the solder pins - and is available at
http://www.digikey.com for about $2.
When reassembling, be sure the pins on the connectors are well
seated and that all cables are routed so that the scope will rotate
360 degrees without snagging anything.
Inside the Fork Arm
Outside the Fork Arm
This photo shows the GPS board and the GPS antenna - click for
larger version pointing out the antenna.
|On newer NexStar GPS telescopes the GPS board is found on the
inside of the fork arm with the hand control bracket or on
the outside of the fork arm with the hand control bracket - there is
no way to tell without removing the plastic covers. The CN-16 GPS unit
also uses this same newer GPS board.
If you didn't find the board inside the base as described above,
try the outside of the fork arm - simply remove the large plastic
cover with the hand control holder. Be sure to unplug the hand
control cable first and set the hand control aside.
If you don't find it there, check the inside of the fork arm.
To remove the cover on the inside of the fork arm, you will first need
to lift up the base cover. Use a 3.5mm or 9/64 inch hex wrench and completely loosen the five
screws securing the plastic base cover - the cover with the Aux, Auto
Guide, and PC ports. It is not necessary to remove the screws as we
will only be lifting the cover, not completely removing it. If you do
remove the screws, note that the one in the back is shorter than the
rest. Then remove the four screws holding the plastic cover on
the inside of the fork arm. Pull the cover free and set it
is held in place by two cross-tip screws. Make a sketch of the
cable connection just to be sure you don't misconnect it later.
Remove the screws (be careful not to drop them into the base) and pull
the board free. Here is the complication - as you will see, the
battery is soldered to the board. At this point, if you are
handy with delicate electronics and don't mind the potential risk of
destroying the board, you can unsolder and replace the battery.
Otherwise, contact Celestron about sending the board to them for
battery replacement. The battery is a Panasonic ML2020-H1CN and is
http://www.digikey.com for less than $3.
For the CN-16 GPS unit,
open the case and you will see the GPS board mounted within.
Again, it is the same as the board in the late model NexStar 8/9.25/11
GPS telescopes and uses the same ML2020-H1C battery, soldered in place.